1. Field of the Invention
The invention relates to mechanized rock crushers and more specifically to a crushing apparatus and method that portably handles reclamation, construction and mining tasks, among other industrial applications.
2. Background Art
Generally stated, a rock crusher is a machine designed to take relatively large rocks as input and produce smaller rocks or rock dust as output. Such machines are often deployed to produce rock fill material for such uses as landscaping and erosion control. Rock crushing machines are typically large, very noisy, and produce a considerable quantity of unwanted dust. Most rock crushing machine installations are therefore in rural areas, away from population centers, and always from where the crushed materials are most needed.
While there are prior art crushers which are adequate for the basic purpose and function for which they have been specifically designed, they tend to be deficient in that they generally fail to provide a relatively efficient, low horsepower, compact crusher that is also practical for other small scale applications apart from traditional mining requirements. Typical rock crushing machines which are capable of reasonable rates of production, tend to be prohibitively large, bulky, and expensive. Most notably, their size, weight, and the horsepower requirements make them expensive and difficult to move crushing operations from one location to another.
It has been observed within the industry that “No crusher has ever been devised that will produce only material exceeding a certain minimum size. There is produced always a substantial portion of material that is crushed to fine for the purposes at hand . . . This explains in part why crushing machines, especially those designed for crushing effectiveness . . . are very rugged and massive.” Gaudin, A. M., Principles of Mineral Dressing, p. 5 (McGraw-Hill, 1939).
Within the state of the art, rock crushing machinery is relatively immobile, usually requiring massive foundations and/or dead weight for stability, usually requiring massive foundations. High costs for haulage and related transport equipment are usually entailed. Crushing relatively small amounts of rock or demolition waste in areas even a short distance from existing crushing plants or installations usually cannot be economically justified. Significant value could be realized with the development of a means to economically crush rock, construction and demolition materials at their source, and in the various quantities that are available and needed.
It has been estimated that approximately ten tons of processed aggregate are produced annually for every man, woman and child in the United States. Land fill volume nationwide includes about 15% of recyclable inorganic material, such as brick and concrete. These materials could be recycled if they were to be economically comminuted on site. Together, these material resources offer opportunities representing huge markets that are ready for technical advancement, innovation, and cost savings.
Rocks may be considered, from the viewpoint of communition to fall into two structural types: homogeneous and heterogeneous. In structurally homogeneous rocks, fracture occurs through mineral grains and along the grain boundaries. Heterogeneous rocks are those in which fracture planes occur only along the grain boundaries. Crushed heterogeneous rock tends to have a greater proportion of particle size near the average grain size than is obtained from structurally homogeneous rocks. Cracks occur when the rock is subjected to external forces which, if sufficient, cause the rock to fracture. It would be desirable to have a fracturing mechanism that is so configured as to reduce the forces that are necessary to cause the rock to fracture. It is known that different closed sets of a jaw crusher generate distinct grade variations and that in general, a smaller closed set produces a greater degree of grade variation and finer particle size. C. W. Lai, et al., “EFFECTS OF GRAIN BOUNDARY FRACTURING ON GRADE VARIATION OF COMMINUTED SLAG”, Trans. Inst. Min. Metall. 111, 307 (2002)
The types of prior art rock crushers include (1) impact crushers (e.g. hammer crushers, rotor impactors, vertical centrifugal impact crushers and cage mill crushers) and (2) compression crushers (e.g., jaw crushers, cone crushers, roll crushers, pen crushers, and gyratory crushers). The type of crusher that is best suited for a given job usually depends on the material to be crushed and the final application of the crushed material, together with maintenance and operational cost considerations. Other consideration factors may include power consumption, vibration, noise, and environmental issues.
Jaw crushers conventionally can handle hard rock, offer favorable reduction ratios, produce desired product characteristics at a reasonable throughput rate and are relatively economical to operate once they are put into place. (As used herein, the term “reduction ratio” refers to the ratio of the average size of raw material at the inlet to the average size of the finished product at the outlet.) But in mines and other locations that have restrictive space requirements, conventional crushers may be too wide or too tall, particularly if the input material is fed vertically downwardly. Another type of feed system, which differs from gravity fed configurations, is provided by horizontally mounted jaw crushers. In those configurations, a horizontal conveyor belt or feeder delivers input material to the lower edge of jaws in order to move material through the machine. Such a configuration however, tends to include a movement of finer material in a direction that opposes the major direction of throughput. This tends to result in a clogging or choking phenomenon. A rotary jaw crusher is described in U.S. Pat. No. 4,165,042. The horizontal feed feature described therein requires that all material must be fed to this unit at an angle of 45 to 50 degrees minimum from horizontal to meet the production requirements of commercial use. Further, conventional jaw crushers typically are not operated at high speed in order to avoid vibration problems propagated by moving jaw components. Such movements tend to cause balancing and vibrational problems.
Related difficulties are not limited to impact crushers. Compression crushers, for example, also are prone to excessive wear. If a region of a roll is worn, material to be crushed tends to be concentrated on the worn portion. If so, the wear rate of that portion tends to accelerate.
Rock crusher machine geometry conventionally defines the term “nip angle”. This geometry relates to the ability to crush rock at a commercial rate. Some crushers built according to prior art tend to eject the materials being fed into the device from the machine, opposite the desired direction of material flow. This creates a noticeable level of inefficiency during the operation of the crushing machines of this design.
In underground mines, the maintenance of road beds can be expensive. The mine may operate conventional transports devices that move waste rock to the surface for handling by large scale crushers. The crushed material may then be returned back down the mine for grading and top dressing. It has been estimated that the typical cost is about $50-$100 per cubic yard. Accordingly, it would be desirable to handle the crushing operation underground, thereby producing a stockpile of material that is ready for applying to the road bed. One such machine is sold by Mining Technologies International Inc.'s (MTI) under the name “HydraCrusher.” This device includes a bucket with a built-in, hydraulically-operated crushing mechanism. Adjustable jaws receive the coarse material. That unit is a fixed jaw and a moving jaw. There are external counterweights, which require guards for operator safety. Typical horsepower requirement may be of the order of 200-300 hp.
Other art identified in a search conducted before filing this patent application are the following U.S patent references: U.S. Pat. Nos. 3,958,767; 4,165,042; 4,288,039; 4,288,040; 4,899,942; 4,909,128; 5,054,958; 5,482,218; 6,446,892; and published application No. 2003/0132328 A1.